Pipelines are typically installed in subterranean trenches although even in-ground trenches can extend through geographical areas having little or no foundational support. Pipelines, particularly those carrying gaseous products can become buoyant in environments such as marshy areas and when under water. Hydrostatic forces and resulting movement of pipelines can cause stress and fatigue which can lead to catastrophic failure.
Typically in cold areas of the world pipelines are installed in winter when such unconsolidated environments are frozen. A trench is formed and the installed pipelines are weighted down with ballast of some sort including concrete and clamp-on weights. Once the environment thaws, the pipeline and weights become subject to hydrostatic forces and the intent is that the pipeline is restrained by the weights.
Most recently ballast is provided in a variety of sacks which avoid damage to a pipeline's protective coatings. Examples of such technology include Canadian Patent 2,277,523 by Jewell implementing a particular strapping embodiment and Canadian Patent 2,076,006 to Connors introducing particular forms of pipeline ballasts using ballast sacks.
Use of sacks, while safer for coated pipelines, are bulky and difficult to secure to the pipeline. Conventional sacks are filled with gravel or sand. The specific gravity of gravel or sand, while substantial, still requires a great volume for providing sufficient ballast. Connors deals with the strength and forces on the sacks with strengthening means and reinforcement means to restrict deformation and control the shape of the sack about the pipeline. Jewell has addressed some difficulties in properly securing gravel-filled sacks to the pipeline to minimize shifting.
Smaller pipelines can be installed into the trench with ballast already on them. The majority of pipeline ballast is strapped to the smaller pipelines before entering the ditch or trench. The weights are loaded on the pipeline and as the pipeline enters the trench on a steep angle the weights could slide down the pipeline and out of position in these conditions.
There is the possibility for shifting of the ballast along or off of the pipeline due to a variety of scenarios including: inadequate securing of the ballast thereto, frost heave, and possibly due to changes the buoyancy of the pipeline
Larger pipelines are typically placed in the trench and ballast added after the fact. The underside of the installed pipeline is then virtually inaccessible which complicates conventional strapping means for securing of ballast.
Further, the sheer bulk of gravel compounds the aforementioned securing difficulties and adds to the time and expense for large excavations to accommodate the gravel ballast, the expense of a multiplicity of virtually continuous side-by-side placement along a pipeline, the labor expense to install so many sacks and high shipping cost to transport so many sacks to the installation point. Further, current sacks require the trench to be dug wide and deep due to the bulk of the sacks and as large sacks over hang below the bottom level of the pipeline.
Thus there continues to be a need for pipeline weights or ballast which resists shifting during hydrostatic, frost heave, steep incline installation conditions and other adverse conditions. The ballast is preferably readily and consistently secured to large diameter pipeline and the configuration of the pipeline ballast minimizes preparation and installation expense.